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Planal Dominance The effects of variations of joint axes positions on lower limb biomechanics
- may explain the difference between the clinical findings of the static examination and dynamic function - to prescribe the angulation of the rearfoot post on a functional foot orthoses - to
help predict how a foot will function with particular orthoses
refer to the section on the subtalar joint at the start of the course manual (and additional reading) Generally considered to be: 16 degrees from the sagittal plane 42 degrees from the transverse plane
BUT -
these are just averages in the reported studies
equal forces needed about both sides of axis for equilibrium this can vary depending on position of STJ axis
(see
diagram shown in the lecture)
(see diagram shown in the lecture) imagine what would happen to the foot if the subtalar joint axis is: a) Horizontal b) Vertical
see figs 8-10 in Green & Carol More vertical axis = more transverse plane motion More horizontal axis = more frontal plane motion This is what the foot will look like: refer
to manual (Green and Carol - figs 16 - 18)
a) Frontal plane compensation b) Transverse plane compensation c) Sagittal plane compensation Refer
to your manual for more information: Green DR & Carol A: Planal
Dominance. Journal of the American Podiatric Medical Association 74(2)98-103
1984
see diagram
the difference between static examination and dynamic evaluation location of symptoms - in the foot or leg choice of type of orthoses selecting
the degree of rearfoot post
refer to the section on the mid-tarsal joint at the start of the course manual (and additional reading)
Longitudinal axis - 15 degrees from the transverse plane and 9 degrees from the sagittal plane Oblique axis - 52 degrees from the from the transverse plane and 57 degrees from the sagittal plane
for more details on this refer to the paper by Anne-Maree Keenan in the course manual - 'Understanding Midtarsal Joint Function - Fact and Fallacy' WHY - teach something that is wrong? BECAUSE - it is still a good model to use so we can understand and explain how the foot functions SO - it is a 'convenient theoretical fiction'
theories are ideas to explain phenomena a theory can assume too much significance - it acts as a barrier to other approaches being considered the midtarsal joint will function independently of any theory about it theories have changed, but the midtarsal joint has not two kinds of approaches in understanding of how theories relate to the universe that they are meant to apply - realist and instrumentalist
believe that science aims at a true description of what the world is really like scientists should formulate theories that depict the true structure of the universe (...or the midtarsal joint) the universe has a true structure that is independent of human theorising about it so true theories correctly describe that reality
In the Kinetic Theory, gases are really made up of molecules that are in random motion that collide with each other and with the walls of the container In classical electromagnetic theory, there really are electric and magnetic fields that obey Maxwell's equations the two axes model of the MTJ is not a realist theory as it does not describe the reality of how the MTJ function
believe that theories are nothing more than computational devices that are useful for the description and prediction of phenomena they are convenient fictions that facilitate understanding and calculations
In the Kinetic theory of gases, moving molecules are convenient fictions that enable scientists to relate and make predictions about the properties of gases In Newtonian mechanics forces are not entities that really exist, but are inventions of the physicist to facilitate understanding and calculations Kekule took an instrumentalist approach when he proposed a closed ring of atoms to explain the molecular behaviour of benzene
Instrumentalist theories may be useful to describe phenomena, but they do not provide evidence for the existence of that phenomena this is why the 2 axes MTJ model is just an instrumentalist theory - it is a convenient theoretical fiction, but does not describe reality
we do not know much about the variations of the longitudinal axis we can get a fairly good idea about the position of the oblique axis of the midtarsal joint
52 degrees 57 degrees
more vertical axis = grief
(see diagram at beginning of course manual) Estimating Sagittal Plane Pitch of the OAMTJ High - large degrees of forefoot abduction with compensatory STJ and OAMTJ pronation Low - small degrees of forefoot adduction with compensatory STJ and OAMTJ pronation Average - between high and low
Can the foot stay on top of the orthosis?
Kirby KA: Methods for Determination of Positional Variation in the Subtalar Joint Axis. Journal of the American Podiatric Medical Association 77(5)228-234 1987 Philips RD & Lidtke RH: Clinical Determination of the Linear Equation for the Subtalar Joint Axis. Journal of the American Podiatric Medical Association 82(1)1-20 1992 Tomaro JE et al: Subtalar Joint Motion and the Relationship to Lower Extremity Overuse Injuries. Journal of the American Podiatric Medical Association 86(9)427-432 1996 Anthony RA: The Manufacture and Use of the Functional Foot Orthosis. Karger 1991 (pg 142) The Midtarsal Joint Axes refer to the section on the mid-tarsal joint at the start of the course manual (and additional reading) |
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Why it is important... 
References